A major agricultural pest, the tomato fruitworm can feed on many different plants. Hence, the species has been given many different common names including cotton bollworm and corn earworm. It has also been known to consume tobacco, legumes, grain sorghum, and other vegetables and fruits.

The pest occurs throughout the Western Hemisphere. In warm areas several generations occur annually. North of Interstate 70 the pupae cannot overwinter in the soil. Most populations enter Missouri as migrating swarms of moths from the southern United States.

Symptoms and Diagnosis

Tomato Fruitworm

The evidence of tomato fruitworm is usually a visible black hole at the base of the fruit stem. When the tomato is cut, tunneling is evident and the cavity may contain frass and decay as well as the worm itself.

Corn Earworm

Most evidence of corn earworm is at the tip of the ear—damaged kernels, frass, the worm itself, and possibly resulting fungal disease.

Life Cycle

The eggs of this pest are each about ½ the diameter of a pinhead. They are spherical with a flattened base and white or cream in color, developing a reddish-brown band just prior to the young hatching. Depending on the temperature, the young hatch in 2-10 days.

The larvae measure 11/2-2 inches when fully grown and may be green, brown, pink, yellow, or even black. They have tan heads and alternating light and dark stripes run lengthwise on the bodies. The skin is coarse and has small, thorn-like projections called tubercles. The larval stage lasts 14-21 days.

When the larvae are finished feeding the worms drop to the ground and enter the soil near the base of the plant where they transform into shiny brown pupae. During summer adults emerge in 10-14 days and start the cycle over. In the fall, south of Interstate 70 the pupae survive winter 2-6 inches below the soil surface. The moths emerge from overwintering pupae during late April and May.

Adult moths are usually light yellow-olive in color with a single dark spot near the center of each forewing. Each forewing has 3 slanted dark bands. Their hind wings are white.

The cycle repeats itself with the moths laying eggs at dusk on host plants on warm days. The total generation time is 28-35 days.

The moths lay eggs on the foliage of the tomato plants. With corn the moths usually lay eggs on corn tassels and silks but the larvae will migrate down the silk to the ear tips within one hour of hatching where they will feed on the developing kernels protected by the husk. When larval development is complete the larvae chew through the husk and drop to the ground to begin the pupal stage.

Integrated Pest Management Strategies

Tomato Fruitworm

1. Sanitation. Collect and dispose of any infested fruit before the insect completes its life cycle.

2. Introduce parasitic wasps. Do not remove parasitized caterpillars. Instead, leave them to assist as a natural, biological control.

3. Dusting with diatomaceous earth may kill larvae.

4. Use of a biological pesticide such as Bt can kill larvae during the warmest months.

5. Use chemical pesticides. The pest has developed a resistance to many pesticides but the following pesticides are often used: esfenvalerate (Asana), methomyl (Lannate), azinphos-methyl (Guthion), carbaryl (Sevin), or pyrethrin. These must be applied before the worm enters the fruit.

6. Minimize local food sources. Avoid planting tomatoes near corn or other hosts of the fruitworm to minimize populations.

Corn Earworm

1. Introduce parasitic wasps as with tomato fruitworm.

2. Use a biological pesticide such as Bt as described above.

3. Use chemical pesticides. With corn earworms the timing of the application is very important because once the larvae move down under the husk they are ineffective. Cyfluthrin can be used. Pheromone traps can be used to monitor moth build-up and determine when to release parasite eggs or apply pesticides.

4. Plant resistant corn hybrids. Plant varieties which produce within the silks the same toxin as Bt and may also have husks which are tight around the ear.

5. Early corn is more likely to escape the peak populations of egg-laying moths.

6. Treat with mineral oil. Place a drop of mineral oil on the silks of the young ears of corn where they enter the husk right after pollination has occurred to trap young caterpillar larvae before they enter the ear.